1. Field of the Invention
The present invention relates to polyurea and polyurea/polyurethane hybrid foams made from N-(polyoxyalkyl) N-(alkyl)amines. These polyurea foams have utility in molded foam applications such as automotive seating as well as in slabstock foam which is often used as carpet underlay or in furniture applications.
2. Prior Art
Urethane technology as practiced today offers end users a versatility unsurpassed by virtually any other polymer technology. Readily available intermediates and processing equipment now allow easy preparation of solid elastomers ranging from very low to very high hardness, and foamed products ranging from one half to thirty pounds per cubic foot in density. The properties of these materials are generally very good, and large markets have evolved around their use.
The products of primary interest in the present invention are foams. Historically, urethane foams have been prepared by carefully controlled reaction of a number of important ingredients including: a polyol, water, an isocyanate, catalysts, silicone surfactant and (optionally) added blowing agent.
Polyols in early systems were generally based on propylene oxide. Improvements in economics and in processing were achieved by adding various amounts of ethylene oxide to these polyols, generally in the polyol backbone. Polyols such as these contained secondary hydroxyl groups, and consequently, were slow to react in the foaming system. Subsequent studies showed that significant improvement in the overall cure characteristics of a given system could be attained by converting some of the secondary hydroxyl groups on the polyol to more highly reactive primary hydroxyls by "capping" the polyol with ethylene oxide rather than placing the ethylene oxide in the backbone. Polyols such as these are described in U.S. Pat. Nos. 3,336,242 and 3,535,307. They have found an important place in the flexible foam industry largely because of their greater reactivity.
Even with the success these materials have enjoyed, areas for improvement remain. One of these is the general area of foam productivity, i.e., reactivity. One way to increase the reactivity in these types of intermediates is to replace the primary hydroxyl groups with the highly reactive amine group. Such polyethers are known in the art and are described in U.S. Pat. 3,654,370. They are primary amine terminated polyethers made by amination of an appropriate polyether polyol with ammonia. Unfortunately, it has proven very difficult to use these highly reactive amines to prepare foams. In fact, several patents teach that these primary amine terminated polyethers are too reactive in various foam applications. See for instance U.S. Pat. Nos. 3,838,076; 3,847,992; and 3,979,364.
Additional art discussing the potential utility of amine polyethers include:
U.S. Pat. No. 3,179,606 focuses on a cellular urethane product from a foamable mixture comprised of a major portion of a polyoxyalkylene polyol, an isocyanate, a catalyst and up to 50 weight percent of a primary amine containing polyamine derived from reaction of a polyglycol and either ammonia or polyalkylene polyamines.
U.S. Pat. No. 3,267,050 teaches a foam from reaction of a polyisocyanate, a blowing agent, a catalyst, and an admixture of a polyol and up to 15% of an amine terminated polyol. The amine is a specially prepared material made by reaction of a conventional polyol with acrylonitrile followed by reduction of the remaining nitrile group to the corresponding primary amine.
U.S. Pat. No. 3,838,076 teaches a cellular polyurethane formed by reacting, in the presence of a blowing agent, an organic polyisocyaaate and a partially aminated polyol wherein 10 to 50% of the hydroxyl groups have been replaced by primary amine groups.
U.S. Pat. 4,286,074 describes graft polymer dispersions of free radically polymerized ethylenically unsaturated monomers in an amine terminated polyoxyalkylene polyether polymer. The amine terminated polyether exemplified are primary or secondary amine containing materials with a maximum equivalent weight of 1000.
Also, the reaction of a primary amine with an alcohol (polyol) is a known approach. However, U.S. Pat. No. 4,686,242 teaches that this approach actually produces an amine terminated polyether where the amine groups are predominantly primary amines.
Two features of the prior art described above are significant relative to the foams which are the subject of this invention. The first is that the amines evaluated in these patents are generally primary amines. The only exception involves U.S. Pat. 4,286,074 where a low molecular weight difunctional amine is disclosed but not evaluated in any application. The second is that these primary amines are never used as 100% of the polyoxyalkylene component. Either the polyether itself is only partially aminated, or the amine terminated polyether is used as a blend in a conventional polyol. One reason for this blend approach may well be the very high reactivity of amine terminated polyethers. Blending with a polyol or using only partial amination would essentially dilute the highly reactive amine, allowing its use. In fact, our recent work confirms it is virtually impossible to prepare a foam using a commercially available 5000 MW primary amine terminated polyether at a level of 100% in the formulation.
Quite unexpectedly, it has been found that a new class of amines identified as N-(polyoxyalkyl)-N-(alkyl)amines can be used to prepare foams using standard preparative techniques. No problems associated with high reactivity were observed. In fact, the foaming system handled more like a conventional polyol foam than one based on a reactive amine. Unlike "urethane" foams prepared using the conventional polyol approach, the foams prepared using N-(polyoxyalkyl)-N-(alkyl)amines can be pure polyurea foams (i.e., the foam contains essentially no urethane bonds in its structural backbone). In addition, these novel new amines can be used in blends with other reactive foam ingredients to provide further reactivity control and hybrid systems.